The correct answer is B) 30°. When anchoring in an area with a hard bottom, the fluke angle of the anchor should be set at 30 degrees. This is because a 30-degree fluke angle provides the best holding power and penetration into a hard seafloor. The anchor's flukes need to bite into the hard bottom at this specific angle to ensure the anchor sets properly and holds the vessel securely in place. The other answer choices are incorrect because a 20-degree fluke angle may not provide enough penetration, while 40-degree and 50-degree angles are too steep and may cause the anchor to bounce or skid across the hard bottom without setting properly.